1. Field of the Invention
The present invention relates to an optical coherence tomography device capable of controlling measuring position, and more particularly, to an optical coherence tomography device which is capable of controlling a working distance between an eye (an object to be examined) and the optical coherence tomography device and capable of accurately center-aligning the eye with the optical coherence tomography device.
2. Background Art
It is necessary to non-invasively obtain photographs of 2-dimensional tomographic (sliced) images of patient's eye for an ophthalmological operation such as a cornea operation or a cataract operation etc. For this, there has been used an optical coherence tomographic apparatus (optical coherence tomography: OCT) by which tomographic images of bio-tissue can be obtained with high resolution of submicrometers.
FIG. 1 shows a block diagram of a tomographic image formation section used in a conventional time domain-optical coherence tomography device (TD-OCT). As shown in FIG. 1, the tomographic image formation section of the TD-OCT has a light source (10), a beam splitter (12), a reference mirror (14) and a photo detector (16). The light source (10) emits a broadband low-coherence light (L) having short coherence length and the beam splitter (12) is for splitting the broadband low-coherence light (L) into a reference light (R) and a signal light (S). The reference mirror (14) moves along the propagation direction of the reference light (R) and reflects the reference light (R). The photo detector (16) detects an interference light (C) which is a superimposed light of the signal light (S) reflected from a specific depth of the sample (18) to be examined (for example, eyeball) and the reference light (R) reflected from the reference mirror (14).
FIG. 2 shows a block diagram of a tomographic image formation section used in another conventional device of spectral domain-optical coherence tomography (SD-OCT). As shown in FIG. 2, the tomographic image formation section of the SD-OCT has a light source (20), a fiber coupler (22), a reference mirror (24) and a photo detector (26). The light source (20) emits a broadband low-coherence light (L) having short coherence length and the fiber coupler (22) divides the broadband low-coherence light (L) into a reference light (R) and a signal light (S). The reference mirror (24) is located fixedly along the propagation direction of the reference light (R) and reflects the reference light (R). The photo detector (26) detects an interference light (C) which is the superimposed light of the signal light (S) reflected from a specific depth of the object to be examined (28) and the reference light (R) reflected from the reference mirror (24). The photo detector (26) has a collimator lens (26a) for collimating the interference light (C), a diffraction grating (26b) for spectrally dividing the interference light (C), a line scan camera (26c) for detecting the spectrally divided interference light (C) and so on. Further, optionally, on the optical path of the signal light (S) are provided a X-scanner (32) and a Y-scanner (30) for moving a target position of the signal light (S) in X-direction and Y-direction respectively on XY-plane, a collimator lens (34) for collimating the signal light (S), and a reflection mirror (36) for changing the optical path of the signal light (S), and so on. The X-scanner (32) and the Y-scanner (30) is for obtaining 2-dimensional or 3-dimensional tomographic images of the object to be examined (28) and may a galvano mirror for scanning the signal in X-direction and Y-direction respectively. With the broadband light source (20), the fixed reference mirror (24), the diffraction grating (26b) and the line scan camera (26c) of the SD-OCT in FIG. 2, tomographic images of bio-tissue can be obtained with high resolution of submicrometers.
The above-mentioned OCTs have been used in a various biomedical fields, such as in obtaining tomographic images of eye (specifically, eyeball), skin endothelial structure, blood flow, teeth, gastro-intestinal tract and so on. When the OCT is used for obtaining tomographic images of eye, before measuring, by adjusting a working distance between the eye to be examined and the OCT, the signal light should be focused and also a center of eye, that is, a center of cornea should be center-aligned with a center of the OCT. In scanning retina by using the OCT, the scanning light of the OCT stops (namely, located) on a pupil of the eye. That is, the scanning lights of all directions are collected in one point of the pupil and then spread out over every parts of the retina. Here, the working distance between the eye to be examined and the OCT should be exactly adjusted. Otherwise, the stop position of the scanning light varies (that is, the scanning light does not located at the pupil center) so that there is generated a vignetting effect which causes a signal loss in obtaining the retina images. For eliminating such vignetting effect, the working distance and the center-alignment should be accurately adjusted. Conventionally, an examiner has adjusted the working distance and aligned the center of the eye while observing the eyeball image with his or her naked eyes, which is dependent on the examiner's experience. Therefore, the conventional art has some drawbacks such that a measuring accuracy is insufficient and then it takes a long time to obtain the tomographic images of the eye.